difficult word : 导师

The dictionary says 导师 means "tutor, teacher, academic adviser", but a big group of Chinese people told me that 导师 is a teacher with a Ph.D (博士) .

So, what does 导师 mean exactly? How is it different than 老师， and are there any academic degree requirements to be a 导师？

I learned a long time ago that when I learn something new about Chinese, I have to confirm it at least once or twice with other sources/people because a lot of false information about Chinese is given out a lot